Packable ceramic beads for bone repair

Abstract

Adherent packed beds of ceramic beads, each comprising a ceramic body coated with a biodegradable polymer, and fabric bags containing such beads in a packed, self-supporting configuration. The polymeric coating provides some resilience to a packed bed of the ceramic beads, and prevents the beads from moving with respect to each other when placed under stress, leading to reduced breakage. The ceramic beads desirably are osteoconductive, and preferably are formed of a ceramic material that is resorbed during bone growth, such as hydroxyapatite, tricalcium phosphate, or mixtures of these materials. The beads may contain, either internally or on their surfaces or both, a bone morphogenic protein, and the latter may also be included in the biodegradable polymer coatings on the beads.

1. An article useful for replacing bone in orthopedic procedures, the article comprising a fabric bag formed of a fabric having openings sized to enable bone growth therethrough, and a plurality of ceramic beads packed within said bag, said beads including beads each comprising a single ceramic body having an outer surface defining a shape having a bulk volume, the outer surfaces of said beads bearing a substantially continuous coating of a biodegradable polymer, said coating enabling said beads to form a coherent, load-supporting mass when subjected to compressive forces to restrain bead breakage due to rubbing together of adjacent beads. 
     
     
       2. The article of  claim 1  wherein said beads have a continuous strong supportive framework of struts providing a plurality of interconnecting interstices defining interconnecting openings extending throughout said volume and opening through the ceramic surface of the beads. 
     
     
       3. The article of  claim 2  wherein said interconnected openings open through said biodegradable polymer coating. 
     
     
       4. The article of  claim 1  wherein said beads are packed together to provide a plurality of openings between said beads and wherein said coatings merge at points of contact between beads. 
     
     
       5. The article of  claim 1  wherein the ceramic body is osteoconductive. 
     
     
       6. The article of  claim 1  wherein the ceramic body comprises hydroxyapatite, tricalcium phosphate, or a mixture thereof. 
     
     
       7. The article of  claim 1  wherein the ceramic body additionally comprises a non-resorbable ceramic. 
     
     
       8. The article of  claim 2  including bone morphogenic protein carried within said interconnected openings. 
     
     
       9. The article of  claim 1  including bone morphogenic protein carried within said coating. 
     
     
       10. The article of any one of  claims 1 - 9  wherein said ceramic body shape is generally spheroidal and wherein said beads are substantially uniform in size. 
     
     
       11. An article useful for replacing bone in orthopedic procedures, the article comprising a fabric bag formed of a fabric having openings sized to enable bone growth therethrough, said bag having packed therein a plurality of ceramic beads each comprising a ceramic body having an outer surface defining a shape having a bulk volume, the outer surfaces of said beads bearing a substantially continuous coating of a biodegradable polymer and said beads having continuous openings between them, said coating enabling said beads, when subjected to compressive forces, to form a coherent, load-supporting mass when said beads are subjected to compressive forces to restrain bead breakage due to rubbing together of adjacent beads. 
     
     
       12. The article of  claim 11  wherein said ceramic bodies are generally spheroidal. 
     
     
       13. The article of  claim 12  wherein said ceramic bodies are substantially uniform in size. 
     
     
       14. An article useful for replacing bone in orthopedic procedures, the article comprising a fabric bag formed of a fabric having openings sized to enable bone growth therethrough, and a plurality of ceramic beads packed within said bag, said beads including beads each comprising a single ceramic body having an outer surface defining a shape having a bulk volume, the outer surfaces of said beads bearing a substantially continuous coating of a biodegradable polymer, said coating enabling said beads to form a coherent, load-supporting mass when subjected to compressive forces to restrain bead breakage due to rubbing together of adjacent beads, said packed beads having continuous openings between beads to provide a first level of porosity, and said ceramic bodies comprising a continuous, strong supportive framework of struts providing a plurality of interconnecting interstices that define interconnecting openings that extend throughout the volume and opening through the ceramic surface of the beads to provide a second level of porosity. 
     
     
       15. A method of forming a bone substitute material comprising the steps of providing beads each formed of a single ceramic body having an outer surface bearing a substantially continuous coating of a biodegradable polymer, and applying to a predetermined volume of the beads a compressive force causing the beads to contact each other and to form a coherent load supporting mass, the coating restraining bead breakage or spalling due to rubbing together of adjacent beads. 
     
     
       16. The method of claim 15, wherein the coating is not greater than about one micrometer in thickness. 
     
     
       17. The method of claim 15, wherein the coating has a thickness of about one micrometer. 
     
     
       18. The method of claim 15, wherein the ceramic body is osteoconductive. 
     
     
       19. The method of claim 15, wherein the ceramic body comprises hydroxyapatite, tricalcium phosphate, or a mixture thereof. 
     
     
       20. The method of claim 15, further including providing bone morphogenic protein on the surface of the coating. 
     
     
       21. The method of claim 15, further including providing bone morphogenic protein within the coating. 
     
     
       22. The method of claim 15, each ceramic body comprising a continuous, strong supportive framework of struts providing a plurality of interconnecting interstices that define interconnecting openings, further including providing bone morphogenic protein within the interconnecting openings of the beads. 
     
     
       23. The method of claim 15, wherein the polymer is a copolymer made of a poly(lactic acid) and a poly(glycolic acid). 
     
     
       24. A method of forming a bone substitute material comprising the steps of providing beads each formed of a single ceramic body having an outer surface bearing a thin, substantially continuous coating of a biodegradable polymer, and applying to a predetermined volume of the beads a compressive force causing the beads to contact each other to form a coherent load supporting mass having continuous openings between the beads, the coating restraining bead breakage or spalling due to rubbing together of adjacent beads and having a thickness of about one micron. 
     
     
       25. The method of claim 24, wherein the ceramic body is osteoconductive. 
     
     
       26. The method of claim 24, wherein the ceramic body comprises hydroxyapatite, tricalcium phosphate, or a mixture thereof. 
     
     
       27. The method of claim 24, further including providing bone morphogenic protein on the surface of the coating. 
     
     
       28. The method of claim 24, further including providing bone morphogenic protein within the coating. 
     
     
       29. The method of claim 24, each bead having a single ceramic body comprising a continuous, strong supportive framework of struts providing a plurality of interconnecting interstices that define interconnecting openings, further including providing bone morphogenic protein within the interconnecting openings of the beads. 
     
     
       30. The method of claim 24, wherein the polymer is a copolymer made of a poly(lactic acid) and a poly(glycolic acid). 
     
     
       31. A method of forming a bone substitute material comprising the steps of providing beads each having a single ceramic body comprising a continuous, strong supportive framework of struts providing a plurality of interconnecting interstices that define interconnecting openings and an outer surface bearing a substantially continuous coating of a biodegradable polymer, and applying to a predetermined volume of the beads a compressive force causing the beads to form a coherent load supporting mass, the coating restraining bead breakage or spalling due to rubbing together of adjacent beads and having a thickness of at least an order of magnitude less than the average opening diameter of the interconnecting openings. 
     
     
       32. The method of claim 31, wherein the ceramic body is osteoconductive. 
     
     
       33. The method of claim 31, wherein the ceramic body comprises hydroxyapatite, tricalcium phosphate, or a mixture thereof. 
     
     
       34. The method of claim 31, further including providing bone morphogenic protein on the surface of the coating. 
     
     
       35. The method of claim 31, further including providing bone morphogenic protein within the interconnecting openings of the beads. 
     
     
       36. The method of claim 31, further including providing bone morphogenic protein within the coating. 
     
     
       37. The method of claim 31, wherein the polymer is a copolymer made of a poly(lactic acid) and a poly(glycolic acid).